Eoin Doyle returned to sink his old side as woeful Pompey fell to a 2-1 loss to Oldham.
Doyle got both goals as the managerless Latics picked up a thoroughly-deserved win at Fratton Park.
It was comfortably the worst performance from the Blues since Kenny Jackett became manager, with owner Michael Eisner watching the game.
Pompey’s problems were compounded by Nathan Thompson being taken off in the first half, after apparently being knocked unconscious in a clash with Drew Talbot.
Doyle had hit the post by the time he put his side in front after 16 minutes, after Craig Davies’ shot deflected off Thompson.
Jamal Lowe hit the post seven minutes before the break, but it got worse two minutes after the restart for the home side.
It was a dreadful moment for Talbot who was caught on the ball, allowing Doyle to clip a finish over Luke McGee.
Pompey never looked like pulling themselves back into the game until Brett Pitman scuffed in Lowe’s cutback in the 90th minute.
To make matters worse there was the sight of a crowd disturbance and supporters taking to the pitch late on a day to forget for Pompey.